The present invention pertains to an apparatus for calculating an effective output voltage of a generator.
In a method for calculating the output voltage of a three-phase generator, detection has been conducted for all the three phases which are rectified after stepping down of output voltages by a transformer. However, the method, which detects an average of output voltages, tends to provide an erroneous result when a voltage waveform varies according to load conditions, namely a load existing case and a load non-existing case, due to distortion. For this reason, it has been difficult to achieve good voltage regulation when the average is introduced as an input for controlling an automatic voltage regulator.
In order to overcome the drawback described above, another method has been introduced, which calculates an effective value by an expression (a), incorporating the number M of instantaneous output voltages that are sampled over a period for a sampling frequency correlated with the selected frequency of an output voltage Vi.                               effective          ⁢                                          ⁢          value                =                              (                                          (                                  1                  /                  M                                )                            ⁢                                                ∑                  i                                ⁢                                  V                  i                  2                                                      )                                1            /            2                                              (        a        )            
Japanese Published Patent Application H10-10163 discloses the related arts.
Although this method is advantageous in calculating a true effective output voltage, the method poses another problem that it can not be appropriately applied to an automatic voltage regulator because it takes too much time, one period, to calculate an effective value for controlling the regulator. The method poses the other problem that it leads to complicated processing conducted by a microcomputer because the time interval for accumulation of data samples varies according to the frequencies of the detected output voltage.